1. Field of the Invention
The present invention relates to a plasma processing apparatus, a plasma processing system, a performance validation system, and an inspection method therefor. The present invention can be suitably applied to a plasma processing apparatus having a plurality of plasma processing units so as to minimize the variation among the plurality of the plasma processing chambers and to improve the deposition characteristics using a power of higher frequencies.
2. Description of the Related Art
FIG. 33 illustrates a typical conventional dual-frequency excitation plasma processing unit which constitutes a plasma processing apparatus and performs a plasma process such as a chemical vapor deposition (CVD) process, a sputtering process, a dry etching process, or an ashing process.
In the plasma processing unit shown in FIG. 33, a matching circuit 2A is connected between a radiofrequency generator 1 and a plasma excitation electrode 4. The matching circuit 2A matches the impedances of the radiofrequency generator 1 and the excitation electrode 4.
Radiofrequency power generated from the radiofrequency generator 1 is supplied to the plasma excitation electrode 4 through the matching circuit 2A and a feed plate 3. The matching circuit 2A is accommodated in a matching box 2 which is a housing composed of a conductive material. The plasma excitation electrode 4 and the feed plate 3 are covered by a chassis 21 made of a conductor.
An annular projection 4a is provided on the bottom face of the plasma excitation electrode (cathode) 4, and a shower plate 5 having many holes 7 comes into contact with the projection 4a below the plasma excitation electrode 4. The plasma excitation electrode 4 and the shower plate 5 define a space 6. A gas feeding tube 17 comprising a conductor is connected to the space 6 and is provided with an insulator 17a at the middle thereof so as to insulate the plasma excitation electrode 4 and the gas source.
Gas from the gas feeding tube 17 is introduced inside a plasma processing chamber 60 composed of a chamber wall 10, via the holes 7 in the shower plate 5. An insulator 9 is disposed between the chamber wall 10 and the plasma excitation electrode (cathode) 4 to provide insulation therebetween. The exhaust system is omitted from the drawing.
A wafer susceptor (susceptor electrode) 8 which holds a substrate 16 and also functions as another plasma excitation electrode is installed inside the plasma processing chamber 60. A susceptor shield 12 is disposed under the wafer susceptor 8.
The susceptor shield 12 comprises a shield supporting plate 12A for supporting the susceptor electrode 8 and a supporting cylinder 12B extending downward from the center of the shield supporting plate 12A. The supporting cylinder 12B extends through a chamber bottom 10A, and the lower portion of the supporting cylinder 12B and the chamber bottom 10A are hermetically sealed with bellows 11.
The shaft 13 and the susceptor electrode 8 are electrically isolated from the susceptor shield 12 by a gap between the susceptor shield 12 and the susceptor electrode 8 and by insulators 12C provided around the shaft 13. The insulators 12C also serve to maintain high vacuum in the plasma processing chamber 60. The susceptor electrode 8 and the susceptor shield 12 can be moved vertically by the bellows 11 so as to control the distance between plasma excitation electrodes 4 and the susceptor electrode 8.
The susceptor electrode 8 is connected to a second radiofrequency generator 15 via the shaft 13 and a matching circuit accommodated in a matching box 14. The chamber wall 10 and the susceptor shield 12 have the same DC potential.
FIG. 34 illustrates another conventional plasma processing unit. Unlike the plasma processing unit shown in FIG. 33, the plasma processing unit shown in FIG. 34 is of a single-frequency excitation type. In other words, radiofrequency power is supplied only to the cathode electrode 4 and the susceptor electrode 8 is grounded. Moreover, the matching box 14 and the radiofrequency generator 15 shown in FIG. 33 are not provided. The susceptor electrode 8 and the chamber wall 10 have the same DC potential.
In these plasma processing units, power with a frequency of approximately 13.56 MHz is generally supplied in order to generate a plasma between the electrodes 4 and 8. A plasma process such as a plasma-enhanced CVD process, a sputtering process, a dry etching process, or an ashing process is then performed using the plasma.
The operation validation and performance evaluation of the above-described plasma processing units have been conducted by actually performing the process such as deposition and then evaluating the deposition characteristics thereof according to following Procedures:
Procedure (1) Deposition Rate and Planar Uniformity
Step 1: Depositing a desired layer on a 6-inch substrate by a plasma-enhanced CVD process.
Step 2: Patterning a resist layer.
Step 3: Dry-etching the layer.
Step 4: Removing the resist layer by ashing.
Step 5: Measuring the surface roughness using a contact displacement meter to determine the layer thickness.
Step 6: Calculating the deposition rate from the deposition time and the layer thickness.
Step 7: Measuring the planar uniformity at 16 points on the substrate surface.
Procedure (2) BHF ERching rate
A resist mask is patterned as in Steps 1 and 2 in (1) above.
Step 3: Immersing the substrate in a buffered hydrofluoric acid (BHF) solution for one minute to etch the layer.
Step 4: Rinsing the substrate with deionized water, drying the substrate, and separating the resist mask using a mixture of sulfuric acid and hydrogen peroxide (H2SO4+H2O2)
Step 5: Measuring the surface roughness as in Step 5 in Procedure (1) to determine the layer thickness after the etching.
Step 6: Calculating the etching rate from the immersion time and the reduced layer thickness.
Procedure (3) Isolation Voltage
Step 1: Depositing a conductive layer on a glass substrate by a sputtering method and patterning the conductive layer to form a lower electrode.
Step 2: Depositing an insulating layer by a plasma-enhanced CVD method.
Step 3: Forming an upper electrode as in Step 1.
Step 4: Forming a contact hole for the lower electrode.
Step 5: Measuring the current-voltage characteristics (I–V characteristics) of the upper and lower electrodes by using probes while applying a voltage up to approximately 200 V.
Step 6: Defining the isolation voltage as the voltage V at 100 pA corresponding 1 μA/cm2 in a 100 μm square electrode.
The plasma processing apparatus has been required to achieve a higher plasma processing rate (the deposition rate or the processing speed), increased productivity, and improved planar uniformity of the plasma processing (uniformity in the distribution of the layer thickness in a planar direction and uniformity in the distribution of the process variation in the planar direction). As the size of substrates has been increasing in recent years, the requirement of planar uniformity has become tighter. Moreover, as the size of the substrate is increased, the power required is also increased to the order of kilowatts, thus increasing the power consumption. Accordingly, as the capacity of the power supply increases, both the cost for developing the power supply and the power consumption during the operation of the apparatus are increased. In this respect, it is desirable to reduce the operation costs.
Furthermore, an increase in power consumption leads to an increase in emission of carbon dioxide which places a burden on the environment. Since the power consumption is increased by the combination of increase in the size of substrates and a low power consumption efficiency, reduction of the carbon dioxide emission is desired.
The density of the plasma generated can be improved by increasing the plasma excitation frequency. For example, a frequency in the VHF band of 30 MHz or more can be used instead of the conventional 13.56 MHz. Thus, one possible way to improve the deposition rate of a deposition apparatus such as a plasma-enhanced CVD apparatus is to employ a higher plasma excitation frequency.
In a plasma processing apparatus having a plurality of the above-described plasma processing units, variation in plasma processing among the plasma processing units and their matching circuits is required to be reduced, so that the plasma processing rate (deposition rate when applied to a deposition process), productivity, and uniformity in the plasma process in the planar direction of a workpiece (planar distribution in the layer thickness) can be made substantially the same among the workpieces plasma-treated in different plasma processing units.
The plasma processing apparatus is also required to yield substantially the same process results by applying the same process recipe specifying external parameters for respective plasma processing units such as gas flow, gas pressure, power supply, and process time.
It is desired to both reduce the time required for adjusting the plasma processing apparatus newly installed or subjected to maintenance to achieve substantially the same process results by applying the same recipe and eliminate the variation among the plurality of plasma processing units, as well as the cost required for such adjustment.
Furthermore, reduction in the variation among the plasma processing units has also been required for a plasma processing system comprising a plurality of such plasma processing apparatuses.
The above-described plasma processing unit is designed to use power with a frequency of approximately 13.56 MHz and is not suited for power of higher frequencies. Specifically, radiofrequency characteristics such as impedance and resonant frequency characteristics of the plasma processing unit as a whole, and more specifically, the radiofrequency characteristics of the plasma processing chamber and the matching circuit have been neglected; consequently, no improvement in the electrical consumption efficiency has been achieved when power of a frequency higher than approximately 13.56 MHz is employed, resulting in decrease in the deposition rate rather than improvement. Moreover, although the density of a generated plasma increases as the frequency increases, the density starts to decrease once its peak value is reached, eventually reaching a level at which glow-discharge is no longer possible, thus rendering further increases in frequency undesirable.
In a plasma processing apparatus and a plasma processing system comprising a plurality of plasma processing apparatuses, the radiofrequency characteristics of the plasma processing units including the matching circuits are defined by their mechanical dimensions such as shape. However, the components constituting the plasma processing unit inevitably have differences in size, etc., due to the mechanical tolerance during manufacture. When these components are assembled to make a plasma processing unit, the tolerance due to the assembly is added to the tolerance in the mechanical dimensions. Furthermore, some portions of the plasma processing chamber may not be measurable after assembly of the components; consequently, whether the plasma chamber as a whole has designed radiofrequency characteristics may not be quantitatively validated. Thus, means for examining the variation in the radiofrequency characteristics of the plasma processing chambers has not been available.
Thus, conventional plasma processing apparatuses suffer from the following disadvantages.
Conventional plasma processing apparatuses and systems are not designed to eliminate the differences in electrical radiofrequency characteristics such as impedance and resonant frequency characteristics among the plasma processing units constituting the plasma processing apparatus or system. Thus, the effective power consumed in the plasma generating spaces of the plasma processing units and the density of the generated plasma vary between different plasma processing units.
As a consequence, uniformity in plasma process results may not be achieved when the same process recipe is applied to these plasma processing units.
In order to obtain uniform plasma process results, external parameters such as gas flow, gas pressure, power supply, process time, and the like must be compared with the process results according to Procedures (1) to (3) described above for each of the plasma processing units so as to determine the correlation between them. However, the amount of data is enormous and it is impossible to completely carry out the comparison.
In order to validate and evaluate the operation of the plasma processing apparatus using Procedures (1) to (3) above, the plasma processing apparatus needs to be operated and deposited substrates need to be examined by an ex-situ inspecting method requiring many steps.
Since such an inspection requires several days to several weeks to yield evaluation results, the characteristics of the plasma-treated substrates processed during that period, supposing that the production line is not stopped, remain unknown during that period. If the performance of the plasma processing apparatus is poor, products not satisfying a required level may be manufactured. In this respect, a method for easily maintaining the operation of the plasma processing apparatus at the required level has been desired.
Moreover, when Procedures (1) to (3) described above are employed to inspect the plasma processing units constituting the plasma processing apparatus or system, the time required for adjusting the plasma processing units so as to eliminate the difference in performance and variation in processing among the plasma processing units to achieve the same process results using the same process recipe may be months. The time required for such adjustment needs to be reduced. Also, the cost of substrates for inspection, the cost of processing the substrates for inspection, the labor cost for workers involved with the adjustment, and so forth are significantly high.